Analyzing Failure Modes Using RBDs in Weibull++

Weibull++ provides the ability to use a
reliability block diagram (RBD) to model series,
parallel and k-out-of-n configurations. In
this article, we will give an example of how to use an
RBD to conduct failure modes analysis.

Background

An electronic device can fail due to six independent
primary failure modes: A, B, C, D, E and F. The
component fails if mode A, mode B or mode F occurs. If mode C,
mode D
or mode E occurs alone, the component does not fail; however,
the component will fail if any two (or more) of these
modes occur (i.e., C and D; D and E; E and C; or C, D
and E). The
objective is to analyze each data set using the
2-parameter Weibull distribution with MLE and to
determine the lower 1-sided 90% confidence interval on
the reliability of this component at 100 hours.

Experiment and Data

The following tables present the
time-to-failure data for these modes (in hours).

Analysis

Step 1: Using Weibull++ 7, the first step is
to create a new data sheet for grouped
times-to-failure data with suspensions.

Step 2: Rename the folio to "Component"
and the data sheet to "Mode A." Enter the data given for
Mode A and use the 2-parameter Weibull
distribution with MLE to calculate the parameters, as
shown next.

Step 3: Insert another
data sheet of the same type named "Mode B," enter the data
given for Mode B and calculate the parameters.
Repeat for the remaining failure modes.

Step 4:
Choose Project > Add Diagram. The diagram that is added to the project
will contain a template block
for each data sheet in the project, as shown next.

Step 5: Build the RBD that describes the
reliability-wise configuration of the failure modes, as
shown next.

Note that the node in the diagram requires 2 of the 3
paths to succeed.

Step 6: Click Calculate to analyze the
diagram.

Then use the Quick Calculation Pad (QCP) to
calculate the reliability at 100 hours with the lower
1-sided 90% confidence bound, as shown next.